1. Field of the Invention
The present invention relates to a stackable ball grid array (BGA) semiconductor package and a fabrication method thereof.
2. Background of the Related Art
Currently, there is an effort to produce a highly integrated semiconductor package having a large number of exterior connections. One example is a BGA semiconductor package in which a plurality of solder balls which are attached to a substrate are used as external terminals. In these BGA packages, a plurality of solder balls are attached to an upper or a lower surface of a substrate by the application of heat. The solder balls, which act as external terminals, are not easily bent or deformed by inpacts with solid objects.
FIG. 1 shows a structure of a background art BGA semiconductor package. As seen in FIG. 1, an elastomer 2 is attached to a center portion of an upper surface of a semiconductor chip 1, and a high strength adhesive resin 3 is formed on the elastomer 2. A plurality of metal traces, which transmit electric signals, are formed on the adhesive resin 3. First ends 4a of the metal traces extend across a top surface of the adhesive resin 3, and second ends 4b of each of the metal traces are connected to chip pads 6 formed on a marginal portion of the upper surface of the semiconductor chip 1. A solder resist 5 covers the metal traces 4a and the adhesive resin 3, except for exposed portions of the first ends 4a of the metal traces, onto which solder balls will be attached. An encapsulant 7, such as a molding resin, covers the upper surface of the semiconductor chip 1, and the portions of the metal traces that are not covered with the solder resist 5. Conductive balls 8 are then attached to the exposed portions of the metal traces to serve as output terminals.
Since the conductive balls are exposed on only one side of the package (in FIG. 1, the conductive balls are exposed at the upper surface thereof), it is impossible to fabricate a stackable package of high mount density.